1. Field of the Invention
The present invention generally relates to a mechanical-to-electrical energy conversion technology and, more particularly, to a swinging apparatus and an energy harvester using the swinging apparatus wherein the swinging frequency can be adjusted automatically and mechanical energy can be converted to electrical energy.
2. Description of the Prior Art
The tires play an important role when the performance and safety of a vehicle is concerned. If the tire condition can be monitored, danger due to tire puncture can be prevented, adaptability of roads can be improved, gasoline consumption can be reduced, lifetime of the tires can be lengthened, and the cost of a vehicle can be reduced. To effectively monitor the tire condition, the tire pressure monitoring system (TPMS) has been adopted by the vehicle industry. According to National Thruway and Highway Traffic Safety Administration (NTHTSA), since 2007, all the cars to be sold in the U.S. have to be equipped with tire pressure monitoring systems, which will soon be the next big thing in the car electronic applications.
The TPMS is used for real-time automatic tire pressure monitoring when the car is moving so as to issue an alarm of a flat or low-pressure tire to insure driving safety. The TPMS is an alarm system for protecting the lives of the driver and the passengers. Statistically, there will be 29,000,000 cars demanded in Europe and 18,000,000 units demanded in Europe by the year of 2010, which leads to a total of 192,000,000 TPMS's. The power consumption of a TPMS is 70 μW as powered by Li batteries. Even though Li batteries provide sufficient energy for monitoring the tire pressure, Li batteries are harmful to the environment. Environment-friendly products are more popular in U.S. and some developed countries in Europe. According to Kyoto Protocol and ROHS, people are encouraged to manufacture environment-friendly products.
Therefore, there have been a number of various energy harvesters to replace the batteries. For example, in U.S. Pat. Pub. No. 2005/0151375, an energy harvester is disclosed to convert mechanical energy to electrical energy to be used in the pressure gauge. Magnetic movement (Faraday's Law) is used in the prior art to convert the kinetic energy into electrical energy. However, power generation by magnetic movement is limited to the moving velocity of the magnetic.
Furthermore, in U.S. Pat. No. 6,407,484, a piezoelectric energy harvester is disclosed to convert rotational energy to electrical energy. The centrifugal force of the rotational element drives the metallic sheet to expand or contract the piezoelectric material to convert strain energy to electrical energy. Moreover, in U.S. Pat. Pub. No. 2004/0075363, piezoelectric cantilever beams are used to convert vibration energy to electrical energy. Piezoelectric cantilever beams with various lengths are used to harvest vibration energy at different frequencies. Moreover, U.S. Pat. No. 7,116,036 and U.S. Pat. No. 7,256,505 also disclose an energy harvester that replaces conventional batteries.